Lubricant composition

ABSTRACT

A lubricating oil composition is used in an internal combustion engine that uses a fuel containing at least one fat and oil of natural fat and oil, hydrotreated natural fat and oil, transesterified natural fat and oil and hydrotreated transesterified natural fat and oil. A sulfur compound containing at least one —C—S—C-bond is added to base oil. A content of sulfur contained in the —C—S—C-bond is 0.3 mass % or less based on a total amount of the compound.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition to beused in an internal combustion engine that uses a fuel originating fromnatural fat and oil.

BACKGROUND ART

These days, environmental regulations are being increasingly tightenedon a global scale, among which fuel efficiency regulations and exhaustemission regulations for automobiles are especially being furthertightened. Demands for tightening of the regulations are derived fromenvironmental issues such as global warming and resource conservationdue to a concern for depletion of petroleum resources.

Meanwhile, plants living on the earth absorb carbon dioxide in the air,water and sunlight to photosynthetically generate carbohydrate andoxygen. So-called biofuel, which is manufactured from plant-based plantoil, has been gathering remarkable attentions because of its effects onreduction of carbon dioxide (a main cause of global warming) andreduction of atmospheric contaminants emitted from automobiles. In linewith an idea of carbon neutral advocating that carbon dioxide generateddue to combustion of plant biomass is not counted as a contributor to anincrease of the global warming gas, ratio at which the biofuel is mixedin hydrocarbon fuel is expected to be increased in the future (forinstance, see Non-Patent Document 1).

Non-Patent Document 1: Koji YAMANE, BIODIESEL—From Deep Fryer to FuelTank (Tokyo-Tosho-Shuppankai, May of 2006)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An important problem in an internal combustion engine, especially in adiesel engine, has been how to reduce environment pollution caused bysuch emission gas components as particulate matters (PM) such as sootand NO_(x). An effective solution is to mount such an exhaust purifyingdevice as a diesel particulate filter (DPF) or an exhaust purifyingcatalyst (oxidization or reduction catalyst) on an automobile. Forexample, soot generated in the diesel engine adheres to the DPF to beremoved by oxidization and combustion.

When the DPF is mounted on the diesel engine, post-injection of fuel isgenerally conducted so as to combust the soot accumulated on the filter.Engine oil is diluted by the fuel due to the post-injection, so thatperformance of the engine oil is expected to be lowered. Particularly,since biofuel can be easily accumulated in the engine oil due to itsproperty and generates polar compounds when degraded and decomposed, thebiofuel may adversely affect corrosion of engine parts such as a piston.Also, the filter is likely to be clogged by a metal oxide, hydrosulfate,carboxylate or the like generated in the combustion. In addition, sincea portion of the used engine oil is combusted and exhausted as exhaustgas, it is preferable that metal content or sulfur content inlubricating oil is as low as possible. Thus, it is preferable todecrease phosphorus content or sulfur content in the lubricating oil inorder to prevent degrading of exhaust gas purifying catalyst.

However, lubricating oil sufficiently adapted for use with biofuel hasnot been provided yet. For example, when content in the lubricating oilsuch as metal content, phosphorus content or sulfur content is simplyreduced, lubricating performance thereof may be lowered despite theintentions. Particularly, since polar compounds are formed when biofuelis degraded and decomposed, the biofuel may accelerate corrosion ofengine parts.

An object of the invention is to provide a lubricating oil compositioncapable of reducing corrosion of engine parts even when biofuel orbiofuel-mixed fuel is used in an internal combustion engine such as adiesel engine.

Means for Solving the Problems

In order to solve the above-mentioned problems, a lubricating oilcomposition as follows is provided according to an aspect of theinvention.

(1) A lubricating oil composition is used in an internal combustionengine that uses a fuel containing at least one fat and oil of naturalfat and oil, hydrotreated natural fat and oil, transesterified naturalfat and oil and hydrotreated transesterified natural fat and oil, inwhich a sulfur compound containing at least one —C—S—C-bond is added tobase oil and a content of sulfur contained in the —C—S—C-bond is 0.3mass % based on a total amount of the compound.(2) The lubricating oil composition according to the aspect of theinvention in which the sulfur compound does not contain a—C—S_(x)—C-bond(where x is an integer of 2 or more)(3) The lubricating oil composition according to the aspect of theinvention further containing an alkaline earth metal-based detergent inan amount of 0.35 mass % or less.(4) The lubricating oil composition according to the aspect of theinvention further containing a phosphorus in an amount of 0.12 mass % orless based on the amount of the composition.(5) The lubricating oil composition according to the aspect of theinvention further containing a sulfate ash in an amount of 1.1 mass % orless.(6) The lubricating oil composition according to the aspect of theinvention further containing at least one of a phenol-based antioxidantand an amine-based antioxidant in an amount of 0.3 mass % or more basedon the total amount of the composition.(7) The lubricating oil composition according to the aspect of theinvention further containing a sulfur in an amount of 0.5 mass % or lessbased on the total amount of the composition.

The lubricating oil composition according to the aspect of the presentinvention is corrosive-resistant to engine parts such as a piston in theinternal combustion engine using biofuel made of natural fat and oil andthe like even when the biofuel is mixed into the engine oil. Inaddition, in the lubricating oil composition according to the aspect ofthe invention, even when used in a diesel engine with a DPF, thelubricating oil composition can reduce residual ash content on the DPF,thereby preventing performance of the DPF from being deteriorated.

Natural fat and oil of the invention is not limited to plant-derived fatand oil but may include animal-derived fat and oil.

BEST MODE FOR CARRYING OUT THE INVENTION

Exemplary embodiment(s) of the invention will be described in detailbelow.

A lubricating oil composition according to the invention is alubricating oil composition used in an internal combustion engine, theinternal combustion engine using a fuel that contains at least one fatand oil of natural fat and oil, hydrotreated natural fat and oil,transesterified natural fat and oil and hydrotreated transesterifiednatural fat and oil.

Although the natural fat and oil may be a variety of animal-derived orplant-derived fat and oil that is generally available in nature, thenatural fat and oil is preferably plant oil that contains ester of fattyacid and glycerin as a major ingredient, examples of which are saffloweroil, soybean oil, canola oil, palm oil, palm kernel oil, cotton oil,coconut oil, rice bran oil, benne oil, castor oil, linseed oil, oliveoil, wood oil, camellia oil, earthnut oil, kapok oil, cacao oil, hazewax, sunflower seed oil, and corn oil.

The hydrotreated natural fat and oil is formed by hydrogenating theabove fat and oil under the presence of a suitable hydrogenatingcatalyst.

The hydrogenating catalyst is exemplified by a nickel-based catalyst, aplatinum family (Pt, Pd, Rh, Ru) catalyst, a cobalt-based catalyst, achrome-oxide based catalyst, a copper-based catalyst, an osmium-basedcatalyst, an iridium-based catalyst, a molybdenum-based catalyst and thelike. Two or more of the catalysts may also be preferably combined to beused as the hydrogenating catalyst.

The transesterified natural fat and oil is ester formed bytransesterifying triglyceride contained in the natural fat and oil underthe presence of a suitable ester-synthesis catalyst. For instance, bytransesterifying lower alcohol and the fat and oil under the presence ofthe ester-synthesis catalyst, fatty acid ester usable as biofuel ismanufactured. The lower alcohol, which is used as an esterifying agent,is exemplified by alcohol having 5 or less carbon atoms such asmethanol, ethanol, propanol, butanol, pentanol. In view of reactivityand cost, methanol is preferable. The lower alcohol is generally used inan amount equivalent to the fat and oil or more.

The hydrotreated transesterified natural fat and oil is formed byhydrogenating the above transesterified fat and oil under the presenceof a suitable hydrogenating catalyst.

The natural fat and oil, the hydrotreated natural fat and oil, thetransesterified natural fat and oil, and the hydrotreatedtransesterified natural fat and oil can be preferably used as mixed fuelby adding the above to fuel formed of hydrocarbon such as light oil.

Base oil used in the lubricating oil composition according to theinvention is not particularly limited but may be suitably selected fromany mineral oil and synthetic oil that have been traditionally used asbase oil of the lubricating oil for the internal combustion engine.

Examples of the mineral oil include: mineral oil refined by processinglubricating oil fractions, which are obtained by vacuum-distillingatmospheric residual oil obtained by atmospherically distilling crudeoil, by at least one of solvent-deasphalting, solvent-extracting,hydrocracking, solvent-dewaxing, catalytic-dewasing and hydrorefining;and mineral oil manufactured by isomerizing wax and GTL (gas-to-liquid)WAX.

On the other hand, examples of the synthetic oil include polybutene,polyolefin (α-olefin homopolymer or copolymer such as ethylene-α-olefincopolymer), various esters (such as polyol ester, diacid ester andphosphoric ester), various ethers (such as polyphenylether), polyglycol,alkylbenzene, and alkyl naphthalene. Among the above, polyolefin andpolyol ester are particularly preferable.

One of the above mineral oil may be singularly used or two or morethereof may be combined to be used as the base oil. In addition, one ofthe above synthetic oil may be singularly used or two or more thereofmay be combined to be used. Further, at least one of the above mineraloil and at least one of the above synthetic oil may be combined for use.

Although viscosity of the base oil subjects to no specific limitationand varies depending on usage of the lubricating oil composition,kinetic viscosity thereof at 100 degrees C. is generally preferably 2 to30 mm²/s, more preferably 3 to 15 mm²/s, much more preferably 4 to 10mm²/s. When the kinetic viscosity at 100 degrees C. is 2 mm²/s or more,evaporation loss is small. When the kinetic viscosity at 100 degrees C.is 30 mm²/s or less, power loss due to viscosity resistance isrestricted, thereby improving fuel efficiency.

As the base oil, oil whose % CA measured by a ring analysis is 3 or lessand whose sulfur content is 50 ppm by mass or less can be preferablyused. The % CA measured by the ring analysis means a proportion(percentage) of aromatic content calculated by the n-d-M method (a ringanalysis). The sulfur content is measured based on JIS (abbreviation forJapanese Industrial Standard) K 2541.

The base oil whose % CA is 3 or less and whose sulfur content is 50 ppmby mass or less exhibits a favorable oxidation stability. Such base oilcan restrict an increase of acid number and a generation of sludge,thereby providing a lubricating oil composition that is less corrosiveto metal. The sulfur content is more preferably 30 ppm by mass or less.The % CA is more preferably 1 or less, further more preferably 0.5 orless.

In addition, viscosity index of the base oil is preferably 70 or more,more preferably 100 or more, much more preferably 120 or more. In thebase oil whose viscosity index is 70 or more, a viscosity change due toa temperature change is small.

In the lubricating oil composition of the invention, a sulfur compoundcontaining at least one —C—S—C-bond is added in the above-described baseoil.

Such a sulfur compound is preferably dissolved or uniformly dispersed inthe base oil of the lubricating oil. Examples of such sulfur compoundmay include sulfurized fat and oil, a sulfurized fatty acid, an estersulfide, an olefin sulfide, a dihydrocarbyl monosulfide, a thiadiazolecompound, a thiophosphate ester (thiophosphite, thiophosphate), analkylthiocarbamoyl compound, a thiocarbamate compound, a thioterpenecompound and a dialkyl thiodipropionate compound. Among these, a sulfurcompound used as a sulfuric antioxidant is preferable.

Herein, the sulfurized fat and oil may be obtained by reacting fat andoil (e.g., lard oil, whale oil, vegetable oil and fish oil) with sulfuror a sulfur-containing compound. A content of the sulfur is notparticularly limited, but 5 to 30 mass % is generally preferable.Concrete examples of the sulfurized fat and oil may include a surfurizedlard, a sulfurized rape seed oil, a sulfurized castor oil, a sulfurizedsoybean oil and a sulfurized rice bran oil. The sulfurized fatty acidmay be exemplified by a sulfurized oleic acid, while the ester sulfidemay be exemplified by a sulfurized methyl oleate, a sulfurized rice branfatty acid octyl and a ditridecyl thiodipropionate.

Examples of the olefin sulfide preferably used according to theinvention include a compound represented by the following formula (1).

R¹—S—R²  (1)

In the formula, R¹ represents an alkenyl group having 2 to 15 carbonatoms, and R² represents an alkyl group or an alkenyl group having 2 to15 carbon atoms.

The compound can be obtained by reacting an olefin having 2 to 15 carbonatoms or a dimer to a tetramer thereof with a sulfurizing agent such assulfur, sulfur chloride and the like. The olefin may preferably bepropylene, isobutene, and diisobutene.

Examples of the dihydrocarbyl monosulfide include a compound representedby the following formula (2).

R³—S—R⁴  (2)

In the formula, R³ and R⁴ each represent an alkyl group or a cyclicalkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20carbon atoms, or an alkyl aryl group having 7 to 20 carbon atoms or anarylalkyl group having 7 to 20 carbon atoms, which may be mutually thesame or different.

Herein, when R³ and R⁴ are alkyl groups, the compound is also referredto as an alkyl sulfide.

Examples of R³ and R⁴ in the formula (2) may include methyl group, ethylgroup, n-propyl group, isopropyl group, n-butyl group, isobutyl group,sec-butyl group, tert-butyl group, various pentyl groups, various hexylgroups, various heptyl groups, various octyl groups, various nonylgroups, various decyl groups, various dodecyl groups, cyclohexyl group,cyclooctyl group, phenyl group, naphthyl group, tolyl group, xylylgroup, benzyl group and phenethyl group.

Examples of the dihydrocarbyl monosulfide may include dibenzylmonosulfide, various dinonyl monosulfides, various didodecylmonosulfides, various dibutyl monosulfides, various dioctylmonosulfides, diphenyl monosulfide and dicyclohexyl monosulfide.

Examples of the thiadiazole compound may preferably include1,3,4-thiadiazole, 1,2,4-thiadiazole compound, and 1,4,5-thiadiazolerepresented by the following formulae (3) to (5).

In the formulae, R⁵ to R⁶ each represent a hydrocarbon group having 1 to20 carbon atoms.

Preferable examples of the thiadiazole compound may include2,5-bis(n-hexyldithio)-1,3,4-thiadiazole,2,5-bis(n-octyldithio)-1,3,4-thiadiazole,2,5-bis(n-nonyldithio)-1,3,4-thiadiazole,2,5-bis-(1,1,3,3-tetramethylbutyldithio)-1,3,4-thiadiazole,3,5-bis(n-hexyldithio)-1,2,4-thiadiazole,3,5-bis(n-octyldithio)-1,2,4-thiadiazole,3,5-bis(n-nonyldithio)-1,2,4-thiadiazole,3,5-bis-(1,1,3,3-tetramethylbutyldithio)-1,2,4-thiadiazole,4,5-bis(n-hexyldithio)-1,2,3-thiadiazole,4,5-bis(n-octyldithio)-1,2,3-thiadiazole,4,5-bis(n-nonyldithio)-1,2,3-thiadiazole and4,5-bis-(1,1,3,3-tetramethylbutyldithio)-1,2,3-thiadiazole.

Examples of the thiophosphate ester may include an alkyltrithiophosphite, an aryl or alkyl aryl thiophosphate, and a zincdilauryldithiophosphate. Particularly, a lauryl trithiophosphite and atriphenyl thiophosphate are preferable.

The alkylthiocarbamoyl compound may be exemplified by a compoundrepresented by the following formulae (6) and (7).

In the formulae, R⁷ to R¹⁰ each represent an alkyl group having 1 to 20carbon atoms. R¹¹ represents an alkylene group having 1 to 20 carbonatoms.

Examples of the alkylthiocarbamoyl compound may preferably include abis(dimethylthiocarbamoyl)monosulfide, abis(dibutylthiocarbamoyl)monosulfide, abis(dimethylthiocarbamoyl)monosulfide, abis(dibutylthiocarbamoyl)monosulfide, abis(diamylthiocarbamoyl)monosulfide, abis(dioctylthiocarbamoyl)monosulfide, and a methylenebis(dibutyldithiocarbamate).

The thiocarbamate compound may be exemplified by, for instance, a zincdialkyldithiocarbamate. The thioterpene compound may be exemplified by,for instance, a reaction product of a phosphorus pentasulfide or pinene.The dialkyl thiodipropionate compound may be exemplified by, forinstance, dilauryl thiodipropionate, or distearyl thiodipropionate.

By adding the sulfur compound as specified above in the lubricating oilcomposition, corrosion of engine parts can be considerably reduced.

However, the content of the above-described sulfur compound is 0.3 mass% or less in terms of sulfur contained in the —C—S—C-bond in thecompound of the total amount of the composition. When the content of thesulfur contained in the —C—S—C-bond is 0.3 mass % or more, corrosion ofthe engine parts may be accelerated. The content of the sulfur ispreferably 0.05 to 0.2 mass %.

Further, the sulfur compound preferably does not contain a—C—S_(x)—C-bond (x is an integer of 2 or more). In addition, a sulfurcompound having a polysulfide structure is not preferable in light ofcorrosivity of engine parts. Especially, under the presence of thebiofuel, an elution amount of copper and lead is increased.

The lubricating oil composition according to the invention preferablycontains an alkaline earth metal-based detergent.

Examples of the alkaline earth metal-based detergent include alkalineearth metal sulfonate, alkaline earth metal phenate, alkaline earthmetal salicylate and a mixture of two or more thereof.

Examples of the alkaline earth metal sulfonate include alkaline earthmetal salt of alkyl aromatic sulfonic acid obtained by sulfonating analkyl aromatic compound having a molecular weight of 300 to 1500(preferably 400 to 700). The alkaline earth metal salt is exemplified bymagnesium salt and/or calcium salt. Particularly, calcium salt ispreferably used.

Examples of the alkaline earth metal phenate include alkaline earthmetal salt of alkylphenol, alkylphenol sulfide and a Mannich reactionproduct of alkylphenol. The alkaline earth metal salt is exemplified bymagnesium salt and/or calcium salt. Particularly, calcium salt ispreferably used.

Examples of the alkaline earth metal salicylate include alkaline earthmetal salt of alkyl salicylic acid, which is exemplified by magnesiumsalt and/or calcium salt. Particularly, calcium salt is preferably used.An alkyl group forming the alkaline earth metal-based detergentpreferably has 4 to 30 carbon atoms. The alkyl group is more preferablya linear or branched alkyl group having 6 to 18 carbon atoms, in which 6to 18 carbon atoms may be in a linear chain or in a branched chain. Thealkyl group may be a primary alkyl group, a secondary alkyl group or atertiary alkyl group.

In addition, the alkaline earth metal sulfonate, alkaline earth metalphenate and alkaline earth metal salicylate may be neutral alkalineearth metal sulfonate, neutral alkaline earth metal phenate and neutralalkaline earth metal salicylate obtained by: directly reacting theabove-described alkyl aromatic sulfonic acid, alkylphenol, alkylphenolsulfide, a Mannich reaction product of alkylphenol, alkyl salicylic acidor the like with alkaline earth metal base exemplified by an oxide or ahydroxide of alkaline earth metal such as magnesium and/or calcium; orconverting the above-described substance into alkali metal salt such assodium salt or potassium salt and subsequently substituting the alkalimetal salt with alkaline earth metal salt. Alternatively, the alkalineearth metal sulfonate, alkaline earth metal phenate and alkaline earthmetal salicylate may be: basic alkaline earth metal sulfonate, basicalkaline earth metal phenate and basic alkaline earth metal salicylateobtained by heating neutral alkaline earth metal sulfonate, neutralalkaline earth metal phenate and neutral alkaline earth metal salicylatewith excess alkaline earth metal salt or alkaline earth metal base underthe presence of water; or overbased alkaline earth metal sulfonate,overbased alkaline earth metal phenate and overbased alkaline earthmetal salicylate obtained by reacting neutral alkaline earth metalsulfonate, neutral alkaline earth metal phenate and neutral alkalineearth metal salicylate with carbonate or borate of alkaline earth metalunder the presence of carbon dioxide gas.

The content of the alkaline earth metal-based detergent is preferably0.35 mass % or less in terms of alkaline earth metal, more preferably0.01 to 0.35 mass %, further more preferably 0.1 to 0.35 mass %. Whenthe content of the alkaline earth metal-based detergent is 0.01 mass %or more, the lubricating oil composition exhibits more excellentoxidation stability, base-number retention and high-temperaturedetergency. On the other hand, when the content of the alkaline earthmetal-based detergent exceeds 0.35 mass %, performance of catalyst forpurifying exhaust gas may be deteriorated. In addition, when such isapplied to a diesel engine with a DPF, an amount of ash content adheringto the DPF may be increased, thereby shortening the life of the DPF.

The lubricating oil composition according to the invention preferablycontains a phenol-based antioxidant and/or an amine-based antioxidant asthe antioxidant.

Examples of the phenol-based antioxidant are:octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate;4,4′-methylenebis(2,6-di-t-butylphenol); 4,4′-bis(2,6-di-t-butylphenol);4,4′-bis(2-methyl-6-t-butylphenol);2,2′-methylenebis(4-ethyl-6-t-butylphenol);2,2′-methylenebis(4-methyl-6-t-butylphenol);4,4′-butylidenebis(3-methyl-6-t-butylphenol);4,4′-isopropylidenebis(2,6-di-t-butylphenol);2,2′-methylenebis(4-methyl-6-nonylphenol);2,2′-isobutylidenebis(4,6-dimethylphenol);2,2′-methylenebis(4-methyl-6-cyclohexylphenol);2,6-di-t-butyl-4-methylphenol; 2,6-di-t-butyl-4-ethylphenol;2,4-dimethyl-6-t-butylphenol; 2,6-di-t-amyl-p-cresol;2,6-di-t-butyl-4-(N,N′-dimethylaminomethylphenol);4,4′-thiobis(2-methyl-6-t-butylphenol);4,4′-thiobis(3-methyl-6-t-butylphenol);2,2′-thiobis(4-methyl-6-t-butylphenol);bis(3-methyl-4-hydroxy-5-t-butylbenzyl)sulfide;bis(3,5-di-t-butyl-4-hydroxybenzyl)sulfide;n-octyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate;n-octadecyl-3-(4-hydroxy-3,5-di-t-butylphenyl)propionate; and2,2′-thio[diethyl-bis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate].Among the above, a bisphenol-based antioxidant and an estergroup-containing phenol-based antioxidant are preferable.

Examples of the amine-based antioxidant are: an antioxidant based onmonoalkyldiphenylamine such as monooctyldiphenylamine andmonononyldiphenylamine; an antioxidant based on dialkyl diphenylaminesuch as 4,4′-dibutyldiphenylamine, 4,4′-dipentyldiphenylamine,4,4′-dihexyldiphenylamine, 4,4′-diheptyldiphenylamine,4,4′-dioctyldiphenylamine and 4,4′-dinonyldiphenylamine; an antioxidantbased on polyalkyldiphenylamine such as tetrabutyldiphenylamine,tetrahexyldiphenylamine, tetraoctyldiphenylamine andtetranonyldiphenylamine; and an antioxidant based on naphthylamine,specifically alkyl-substituted phenyl-α-naphtylamine such asα-naphthylamine, phenyl-α-naphthylamine, butylphenyl-α-naphthylamine,pentylphenyl-α-naphthylamine, hexylphenyl-α-naphthylamine,heptylphenyl-α-naphthylamine, octylphenyl-α-naphthylamine andnonylphenyl-α-naphthylamine. Among the above, a dialkyldiphenylamine-based antioxidant and a naphthylamine-based antioxidantare preferable.

Incidentally, as another antioxidant, a molybdenum-amine complex-basedantioxidant may be used. As the molybdenum-amine complex-basedantioxidant, a hexahydric molybdenum compound, an example of which is areaction product obtained by reacting molybdenum trioxide and/ormolybdenum acid with an amine compound, may be used. The reactionproduct may be, for example, a compound obtained by the manufacturingmethod disclosed in JP-A-2003-252887. The amine compound to be reactedwith the hexahydric molybdenum compound subjects to no particularlimitation, and examples thereof are monoamine, diamine, polyamine andalkanolamine. Specific examples of the amine compound are: alkyl aminehaving an alkyl group of 1 to 30 carbon atoms (the alkyl group maycontain a linear chain or a branched chain), exemplified by methylamine,ethylamine, dimethylamine, diethylamine, methylethylamine,methylpropylamine and the like; alkenyl amine having an alkenyl group of2 to 30 carbon atoms (the alkenyl group may contain a linear chain or abranched chain), exemplified by ethenylamine, propenylamine,butenylamine, octenylamine and oleylamine; alkanol amine having analkanol group of 1 to 30 carbon atoms (the alkanol group may contain alinear chain or a branched chain), exemplified by methanolamine,ethanolamine, methanolethanolamine and methanolpropanolamine;alkylenediamine having an alkylene group of 1 to 30 carbon atoms,exemplified by methylenediamine, ethylenediamine, propylenediamine andbutylenediamine; polyamine such as diethylenetriamine,triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine;a heterocyclic compound obtained by reacting monoamine, diamine andpolyamine with a compound having an alkyl or alkenyl group of 8 to 20carbon atoms or imidazoline, monoamine, diamine and polyamine beingexemplified by undecyldiethylamine, undecyldiethanolamine,dodecyldipropanolamine, oleyldiethanolamine, oleylpropylenediamine andstearyltetraethylenepentamine; an alkylene-oxide adduct of thecompounds; and a mixture thereof. In addition, sulfur-containingmolybdenum complexes of succinimide as disclosed in JP-B-03-22438 andJP-A-2004-2866 may be used.

A mixing content of the antioxidant is preferably 0.3 mass % or morebased on the total amount of the composition, more preferably 0.5 mass %or more. When the content exceeds 2 mass %, the antioxidant may not bedissolved in the base oil of the lubricating oil. Accordingly, thecontent of the antioxidant is preferably in a range from 0.3 to 2 mass %based on the total amount of the composition.

The lubricating oil composition according to the invention may be addedas necessary with other additives such as a viscosity index improver, apour point depressant, an antiwear agent, an ashless-type frictionmodifier, a rust inhibitor, a metal deactivator, a surfactant and anantifoaming agent as long as advantageous effects of the invention arenot hampered.

Examples of the viscosity index improver are polymethacrylate, dispersedpolymethacrylate, an olefin-based copolymer (such as anethylene-propylene copolymer), a dispersed olefin-based copolymer, astyrene-based copolymer (such as a styrene-diene copolymer and astyrene-isoprene copolymer). In view of blending effects, a content ofthe viscosity index improver is 0.5 to 15 mass % based on the totalamount of the composition, preferably 1 to 10 mass %.

Examples of the pour point depressant include polymethacrylate having amass average molecular weight of 5000 to 50000.

Examples of the antiwear agent are: sulfur-containing compounds such aszinc dithiophosphate, zinc dithiocarbamate, zinc phosphate, disulfides,sulfurized olefins, sulfurized fats and oils, sulfurized esters,thiocarbonates, thiocarbamates (such as Mo-DTC) and the like;phosphorus-containing compounds such as phosphite esters, phosphateesters, phosphonate esters and amine salts or metal salts thereof; and asulfur and phosphorus-containing antiwear agent such as thiophosphiteesters, thiophosphate esters (such as Mo-DTP), thiophosphonate estersand amine salts or metal salts thereof. However, it should be noted thatthe antiwear agent as described above may accelerate corrosion of theengine parts when being used with the sulfur compound according to theinvention.

Examples of the ashless-type friction modifier include a mono-type orbis-type polybutenyl succinimide and/or a boride thereof, a benzylamine,and a polyalkenylamine. The polybutenyl succinimide having a polybutenylgroup having a mass average molecular weight of 700 to 3500 ispreferable. Other examples of the ashless-type friction modifier arefatty acid, aliphatic alcohol, aliphatic ether, aliphatic ester,aliphatic amine and aliphatic amide, which have at least one alkyl oralkenyl group of 6 to 30 carbon atoms in the molecule.

An ashless dispersant is preferably added in a range from 0.5 to 10parts by mass relative to 100 parts by mass of the base oil.

Examples of the rust inhibitor are petroleum sulfonate, alkylbenzenesulfonate, dinonylnaphthalene sulfonate, alkenyl succinic ester,multivalent alcohol ester. In view of blending effects, a content of therust inhibitor is generally 0.01 to 1 mass % based on the total amountof the composition, preferably 0.05 to 0.5 mass %.

Examples of the metal deactivator (copper corrosion inhibitor) arebenzotriazole-based compounds, tolyltriazole-based compounds,thiadiazole-based compounds, imidazole-based compounds, andpyrimidine-based compounds. Among the above, the benzotriazole-basedcompounds are preferable. By adding the metal deactivator, the engineparts can be prevented from being metallically corroded and degraded dueto oxidation. Such a metal deactivator is preferably used with thesulfur compound as specified above.

In view of blending effects, a content of the metal deactivator ispreferably 0.01 to 0.1 mass % based on the total amount of thecomposition, more preferably 0.03 to 0.05 mass %.

Examples of the surfactant are nonionic surfactants based onpolyalkylene glycol such as polyoxyethylenealkylether,polyoxyethylenealkylphenylether and polyoxyethylenealkylnaphthylether.

Examples of the antifoaming agent are silicone oil, fluorosilicone oil,fluoroalkylether. In view of a balance between antifoaming effects andeconomic efficiency, a content of the antifoaming agent is preferablyapproximately 0.005 to 0.1 mass % of the total amount of the compound.

Sulfur content of the lubricating oil composition according to theinvention is preferably 0.5 mass % or less based on the total amount ofthe composition, more preferably 0.3 mass % or less, further morepreferably 0.2 mass % or less. When the sulfur content is 0.5 mass % orless, deterioration of the catalyst performance for purifying exhaustgas can be effectively prevented.

Phosphorus content of the lubricating oil composition according to theinvention is preferably 0.12 mass % or less based on the total amount ofthe composition, more preferably 0.1 mass % or less. When the phosphoruscontent is 0.12 mass % or less, deterioration of the catalystperformance for purifying exhaust gas can be effectively prevented.

Sulfate ash content of the lubricating oil composition according to theinvention is preferably 1.1 mass % or less, more preferably 1 mass % orless. When the sulfate ash content is 1.1 mass % or less, deteriorationof the catalyst performance for purifying exhaust gas can be effectivelyprevented. In addition, in a diesel engine, ash content accumulated onthe filter of the DPF can be reduced, thereby preventing the filterblockage due to the ash and contributing to a long life of the DPF. Thesulfate ash content means ash content obtained by adding sulfuric acidto carbonized residue caused by combustion of samples for heating sothat the residue has a constant mass. The sulfate ash is generally usedto know a rough amount of metal-based additives contained in thelubricating oil composition. Specifically, the sulfate ash is measuredby a method prescribed in “5. Experiment Method of Sulfate Ash” of JIS K2272.

Incidentally, when vaporizability of lubricating oil in an internalcombustion engine is increased, more lubricating oil is consumed, whichleads to a shortened lifetime of the lubricating oil. In addition,because more lubricating oil is dispersed within the exhaust gascatalyst, catalyst performance is lowered and catalyst lifetime isshortened. In view of the above, in the lubricating oil composition ofthe invention, NOACK evaporation measured according to JPI (abbreviationfor Japan Petroleum Insititute, the same applies hereinafter)-5S-41-93is preferably 15 mass % or less, more preferably 13 mass % or less, andfurther preferably 10 mass % or less.

EXAMPLES

Next, the invention will be further described in detail based onExamples, which by no means limit the invention.

Examples 1 to 2 and Comparatives 1 to 4

Lubricating oil compositions containing components shown in Table 1respectively were prepared, which were then subjected to such acorrosivity test as follows. The components used for preparing thelubricating oil compositions were as follows.

(1) Base Oil: hydrorefining base oil; kinetic viscosity at 40 degrees C.of 20.4 mm²/s; kinetic viscosity at 100 degrees C. of 4.28 mm²/s;viscosity index of 116; % CA of 0.0; and sulfur content less than 20 ppmby mass(2) Viscosity Index Improver: OCP; and mass average molecular weight of800,000(3) Pour Point Depressant: polyalkylmethacrylate; and mass averagemolecular weight of 60,000(4) Metal-Based Detergent: overbased calcium salicylate; base number of225 mg KOH/g (perchloric acid method); calcium content of 7.8 mass %;and sulfur content of 0.3 mass %(5) Polybutenyl Succinic Monoimide A: number average molecular weight ofa polybutenyl group being 1000; nitrogen content of 1.2 mass %; andboron content of 1.3 mass %(6) Polybutenyl Succinic Bisimide B: number average molecular weight ofthe polybutenyl group being 2,000; nitrogen content of 1.2 mass %(7) Phenol-Based Antioxidant:octadecyl-3-(3,5-tert-butyl-4-hydroxyphenyl)propionate.(8) Amine-Based Antioxidant: dialkyl diphenylamine; and nitrogen contentof 4.62 mass %(9) Zinc Dialkyl Dithio Phosphate: Zn content of 9.0 mass %; phosphoruscontent of 8.2 mass %; sulfur content of 17.1 mass %; and the alkylgroup being a mixture of a secondary butyl group and a secondary hexylgroup(10) Sulfuric Antioxidant A: methylene bis(dibutyldithiocarbamate).(11) Sulfuric Antioxidant B: ditridecyl thiodipropionate.(12) Sulfuric Antioxidant C: di-t-dodecyl trisulfide

(13) Sulfuric Antioxidant D: MoDTC

(14) Copper Corrosion Inhibitor:1-[N,N-bis(2-ethylhexyl)aminomethyl]methyl benzotriazole.(15) Antifoaming Agent: silicone antiforming agent

The measurement of properties of the lubricating oil compositions andthe corrosivity test were conducted in the following manner.

(Calcium Content)

Measurement was conducted based on JPI-5S-38-92.

(Sulfur Content)

Measurement was conducted based on JIS K2541.

(Phosphorus Content)

Measurement was conducted based on JPI-5S-38-92.

(Sulfate Ash Content)

Measurement was conducted based on JIS K2272.

(Corrosivity Test)

As the lubricating oil composition to be tested, mixed oil in whichbiofuel (fuel obtained by transesterifying canola oil with methylalcohol) was mixed by 10 mass % of each of the lubricating oilcompositions (new oil) was used, assuming a mixing ratio of the fuel andthe lubricating oil in an internal combustion engine.

In the corrosivity test, 100 g of the mixed oil was put as sample oilinto a glass container (having a diameter of 40 mm and a height of 300mm) and then air was blown into the glass container for 168 hours at 88ml/min while the temperature of the oil is maintained at 125 degrees C.Subsequently, amounts of copper (Cu) and lead (Pb) eluted in the sampleoil were measured by Inductively Coupled Plasma Atomic EmissionSpectroscopy (ICP).

In Reference Examples, the corrosivity test was also conducted using thelubricating oil composition that did not contain biofuel.

The properties of the lubricating oil compositions and the results ofthe corrosivity test are shown in Table 1.

TABLE 1 EXAMPLE 1 EXAMPLE 2 COMPARATIVE 1 COMPARATIVE 2 COMPOSITION BASEOIL 80.40 79.30 80.65 80.30 (mass %) VISCOSITY INDEX IMPROVER 4.00 4.004.00 4.00 POUR POINT DEPRESSANT 0.20 0.20 0.20 0.20 METAL-BASEDDETERGENT 2.60 2.60 2.60 2.60 POLYBUTENYL SUCCINIC MONOIMIDE A 1.60 1.601.60 1.60 POLYBUTENYL SUCCINIC BISIMIDE B 7.80 7.80 7.80 7.80PHENOL-BASED ANTIOXIDANT 1.10 1.10 1.10 1.10 AMINE-BASED ANTIOXIDANT0.50 0.50 0.50 0.50 ZINC DIALKYL DITHIO PHOSPHATE 1.20 1.20 1.20 1.20SULFURIC ANTIOXIDANT A 0.25 0.00 0.00 0.00 SULFURIC ANTIOXIDANT B 0.001.35 0.00 0.00 SULFURIC ANTIOXIDANT C 0.00 0.00 0.00 0.35 SULFURICANTIOXIDANT D 0.00 0.00 0.00 0.00 COPPER CORROSION INHIBITOR 0.05 0.050.05 0.05 ANTIFORMING AGENT 0.30 0.30 0.30 0.30 TOTAL 100.00 100.00100.00 100.00 CHARACTERISTICS CALCIUM CONTENT (mass %) 0.22 0.22 0.220.22 OF COMPOSITION SULFUR CONTENT (mass %) 0.35 0.33 0.25 0.33PHOSPHORUS CONTENT (mass %) 0.11 0.11 0.11 0.11 SULFATE ASH CONTENT(mass %) 1.02 1.02 1.02 1.02 SUF|LFUR CONTENT BASED ON 0.10 0.08 0.000.08 —C—S—C—BOND (mass %) CORROSIVITY TEST Cu ELUTION AMOUNT (mass ppm)6 6 11 31 Pb ELUTION AMOUNT (mass ppm) 43 32 77 158 REFERENCE REFERENCECOMPARATIVE 3 COMPARATIVE 4 EXAMPLE 1 EXAMPLE 2 COMPOSITION BASE OIL80.00 79.65 80.65 80.30 (mass %) VISCOSITY INDEX IMPROVER 4.00 4.00 4.004.00 POUR POINT DEPRESSANT 0.20 0.20 0.20 0.20 METAL-BASED DETERGENT2.60 2.60 2.60 2.60 POLYBUTENYL SUCCINIC MONOIMIDE A 1.60 1.60 1.60 1.60POLYBUTENYL SUCCINIC BISIMIDE B 7.80 7.80 7.80 7.80 PHENOL-BASEDANTIOXIDANT 1.10 1.10 1.10 1.10 AMINE-BASED ANTIOXIDANT 0.50 0.50 0.500.50 ZINC DIALKYL DITHIO PHOSPHATE 1.20 1.20 1.20 1.20 SULFURICANTIOXIDANT A 0.00 1.00 0.00 0.00 SULFURIC ANTIOXIDANT B 0.00 0.00 0.000.00 SULFURIC ANTIOXIDANT C 0.00 0.00 0.00 0.35 SULFURIC ANTIOXIDANT D0.65 0.00 0.00 0.00 COPPER CORROSION INHIBITOR 0.05 0.05 0.05 0.05ANTIFORMING AGENT 0.30 0.30 0.30 0.30 TOTAL 100.00 100.00 100.00 100.00CHARACTERISTICS CALCIUM CONTENT (mass %) 0.22 0.22 0.22 0.22 OFCOMPOSITION SULFUR CONTENT (mass %) 0.31 0.65 0.25 0.33 PHOSPHORUSCONTENT (mass %) 0.11 0.11 0.11 0.11 SULFATE ASH CONTENT (mass %) 1.021.02 1.02 1.02 SUF|LFUR CONTENT BASED ON 0.06 0.04 0.00 0.08 —C—S—C—BOND(mass %) CORROSIVITY TEST Cu ELUTION AMOUNT (mass ppm) 68 300 8 6 PbELUTION AMOUNT (mass ppm) 488 42 75 70

[Evaluation Results]

As is understood from the results of the corrosivity test shown in Table1, Examples 1 and 2 in which the lubricating oil composition accordingto the invention was used produced a slight amount of copper (Cu) andlead (Pb) eluted in the oil even when the lubricating oil composition towhich biofuel was added was used. Especially, it should be noted thatthe elution amount of lead was small as compared with that in thelubricating oil composition to which no biofuel was added as inReference Examples 1 and 2.

On the other hand, when the specified sulfur compound of the inventionwas not mixed as in Comparative 1, the elution amounts of copper andlead were increased. In addition, even when the sulfur compound wasmixed, the elution amounts of copper and lead were increased when thesulfur compound was polysulfide or the like as in Comparatives 2 and 3.

Further, even when the specified sulfur compound was mixed, the elutionamount of copper was increased when the amount of the sulfur compoundwas too large as in Comparative 4.

INDUSTRIAL APPLICABILITY

This lubricating oil composition according to the present invention isfavorably applied to an internal combustion engine in which biofuel orbiofuel-mixed fuel is employed.

1. A lubricating oil composition comprising: at least one fat and oilselected from the group consisting of natural fat and oil, hydrotreatednatural fat and oil, transesterified natural fat and oil andhydrotreated transesterified natural fat and oil; and a sulfur compoundcomprising at least one —C—S—C-bond, wherein a content of sulfur in thesulfur compound with the at least one —C—S—C-bond is 0.3 mass % or lessbased on a total amount of the composition.
 2. The lubricating oilcomposition according to claim 1, wherein the sulfur compound does notcomprise a —C—S_(x)—C-bond, wherein x is an integer of 2 or more.
 3. Thelubricating oil composition according to claim 1, further comprising analkaline earth metal-based detergent in an amount of 0.35 mass % orless.
 4. The lubricating oil composition according to claim 1, furthercomprising phosphorus in an amount of 0.12 mass % or less based on atotal amount of the composition.
 5. The lubricating oil compositionaccording to claim 1, further comprising a sulfate ash in an amount of1.1 mass % or less.
 6. The lubricating oil composition according toclaim 1, further comprising at least one selected from the groupconsisting of a phenol-based antioxidant and an amine-based antioxidantin an amount of 0.3 mass % or more based on a total amount of thecomposition.
 7. The lubricant oil composition according to claim 1,further comprising sulfur in an amount of 0.5 mass % or less based on atotal amount of the composition.
 8. The lubricating oil compositionaccording to claim 2, further comprising an alkaline earth metal-baseddetergent in an amount of 0.35 mass % or less.
 9. The lubricating oilcomposition according to claim 2, further comprising phosphorous in anamount of 0.12 mass % or less based on a total amount of thecomposition.
 10. The lubricating oil composition according to claim 3,further comprising phosphorous in an amount of 0.12 mass % or less basedon a total amount of the composition.
 11. The lubricating oilcomposition according to claim 8, further comprising phosphorous in anamount of 0.12 mass % or less based on a total amount of thecomposition.
 12. The lubricating oil composition according to claim 2,further comprising a sulfate ash in an amount of 1.1 mass % or less. 13.The lubricating oil composition according to claim 3, further comprisinga sulfate ash in an amount of 1.1 mass % or less.
 14. The lubricatingoil composition according to claim 8, further comprising a sulfate ashin an amount of 1.1 mass % or less.
 15. The lubricating oil compositionaccording to claim 4, further comprising a sulfate ash in an amount of1.1 mass % or less.
 16. The lubricating oil composition according toclaim 9, further comprising a sulfate ash in an amount of 1.1 mass % orless.
 17. The lubricating oil composition according to claim 10, furthercomprising a sulfate ash in an amount of 1.1 mass % or less.
 18. Thelubricating oil composition according to claim 11, further comprising asulfate ash in an amount of 1.1 mass % or less.